Eufy SoloCam S220 Replacement Battery 3.7V 5200mAh Li-ion

Eufy S220 SoloCam — 3.7V Li-ion Replacement Battery (SW18650 34M 2P)

This 3.7V, 5200mAh Li-ion battery replaces the original cell in the Eufy S220 SoloCam wireless outdoor security camera. It fits the T3814 and AKT8223 platforms used across the 2K Solar and Night Vision variants. Voltage and capacity match the OEM spec exactly — no adapter or modification needed.

• S220 SoloCam platform fit: The T3814 and AKT8223 boards share the same 3.7V cell format, connector pinout, and BMS handshake logic. One cell covers all variants listed — no wiring changes, no firmware conflict.
• Bench tested on actual hardware: We ran this cell through motion-trigger cycles on a T3814 unit. The BMS passed current correctly during IR LED and processor combined draw spikes without tripping. Charge acceptance from the onboard solar controller was clean across the full charge curve.
• First-install power cycle: After fitting the new cell, power cycle the camera once through the Eufy app. The firmware must register the new cell before motion-recording events log correctly to cloud storage — skip this step and early clips may not upload.

Solar panel not recovering a depleted S220 cell in winter

The S220's solar controller uses a minimum input voltage threshold before it will push charge into a depleted cell. In winter, reduced panel output — especially on overcast days — can fall below that re-entry point, leaving the battery stuck at low voltage. The BMS will not accept charge until the panel delivers enough sustained voltage to cross that threshold. USB-charge the cell to at least 3.5V first, then remount and let the solar panel take over from there.

App showing 0% or incorrect percentage after battery swap

The S220 uses a voltage-threshold indicator, not a fuel gauge IC — it reads state of charge from cell voltage at fixed intervals, not from coulomb counting. A freshly installed cell that hasn't completed a full charge cycle can sit at a voltage that maps to the wrong percentage bucket. Run one complete charge to 4.2V through the app before trusting the readout. After that first full cycle, the displayed percentage will track accurately against actual cell voltage.